I have bar end shifters with friction derailluers. My current setup is 6speed 13 to 34 tooth rear cassette. I am looking at 7 speed brifters/ergos to change to. Can I use 7 speed shifters with 6 speed cassette or do I have to go to a seven speed cassette. Also any recomendations for derailluers... long or medium cage and I want to keep the bike set up as a double on the front. I might convert to 9 speed so anyone have experiance with JensonUSA.com prebuilt wheels.
if your 6 speed is "ultra" spaced (5 cm c/c) then the 7 speed shifters will index correctly. Otherwise you'll have some issues. I don't think they made any 6s ultra cassettes, only 6s ultra freewheels. Most 6s cassettes are Uniglide, too, limiting your 7s cassette options.
Long cage RD: buy the Deore from Nashbar currently @ $17.99. Can't beat it.
If you're going to buy a new wheel, buy a 8/9/10s compatible freehub body and a 4.5mm spacer to place before your 7s cassette. In this case you'll be Hyperglide and open to all cog sizes.